For example, in Patent Literature 1, there is disclosed a technology in which a low-performance disk array system is coupled to a high-performance disk array system, the high-performance disk array system virtualizes a logical volume inside the low-performance disk array system and provides this logical volume to a host device.
Furthermore, in Patent Literature 2, there is disclosed multiple intercoupled RAID (Redundant Array of Independent (or Inexpensive) Disks) controllers, and a technique for transferring data between multiple RAID controllers
Citation List
Patent Literature
    [PTL 1]    U.S. Pat. No. 7,441,095    [PTL 2]    U.S. Pat. No. 6,658,478